CHAPTER III.

DEVELOPMENT AND ITS RESULTS.

We now proceed to enquire whether the abstract conclusions of the last chapter are confirmed by the results of practical experience.

Evidence of this description, to be of value, must not be based on a few cases of doubtful authenticity, or on phenomena whose significance is imperfectly understood, but on results so clear, general, and uniform as to justify the conclusion that they are the expression of all-pervading natural laws.

The weight and quality of such evidence are fully recognised by Mr Herbert Spencer in his 'Principles of Biology,' where (No. X. p. 242) he says:

"Excluding those inductions that have been so fully verified as to rank with exact science, there are no inductions so trustworthy as those which have undergone the mercantile test. When we have thousands

of men whose profit or loss depends on the truth of the inferences they draw from simple and repeated observations; and when we find that the inferences arrived at, and handed down from generation to generation of those deeply interested observers, have become an unshakable conviction, we may accept it without hesitation."

Now, evidence of this character is provided by the uniform experience of skilful breeders of all domestic animals; but we shall deal only with the breeding of cattle, because the various races are closely allied, their habits and appearance are generally known, their mating is closely controlled, their pedigrees are well authenticated, and numerous families or herds are bred under different conditions throughout the country. Cattle-breeding, in short, provides wider and more trustworthy results than can be had of any other domestic race.

Theoretically the object of selective breeding is to develop the fullest expression of the type of the race, and its practice consists in carefully selecting for breeding purposes animals that, in the breeder's judgment, possess the best expression of the type; and so again with their progeny.

The animals selected are carefully pro

tected from any struggle for existence that is, they are kept in comfort and fully supplied with suitable food, but otherwise under natural conditions. By such systematic breeding any cross-blood in the herd is practically eliminated in a few generations; and by selecting the most vigorous animals and developing their progeny under the most favourable conditions, a full expression of type is evolved.

So treated, the herd of the successful breeder will in a few generations approximate, perhaps as closely as it ever will, to a full expression of the type. There were as good specimens of our pedigreed breeds of cattle fifty years ago as there are to-day.

Selective breeding has been steadily prosecuted for three-quarters of a century, and has brought about a higher average expression of type among cattle generally than formerly obtained, but there has been no tendency to specific variation in type. On the contrary, the invariable experience has been that the longer selective breeding is pursued, the more firmly established becomes the family expression of a herd, and the more forcibly do the parents stamp the family likeness on their progeny.

But with improved expression of type the

breeder finds himself in the presence of unexpected obstacles to further development, and they prove insurmountable. If the young stock go unmated to the age when cattle not highly bred reach puberty, the animals, whether male or female, will probably prove infertile, and that without any obvious cause.

The breeder also finds that development has so stimulated precocity that cases have been known where a female only eleven months old has produced a calf; and such cases at thirteen months are not uncommon.

The dam of eleven months had conceived when a calf only two months old, instead of at fifteen to eighteen months-the usual age of puberty among animals not highly bred.

In these circumstances the breeder seeks to avoid sterility in the mature animals by breeding from his young stock when barely half grown. But as the immature dam cannot be fully protected in the struggle between her own growth and that of her unborn calf, both suffer, and both fail to equal their progenitors in development. Practically, a full expression of the type has been reached, and, to maintain the existence of the herd, its standard of excellence must be lowered by immature mating.

Development by selection and protection from the struggle for existence is thus limited by sterility or precocity.

The results of experience, therefore, confirm our abstract deductions

That the development of a type cannot exceed a full expression of the energy of its life-forces; and

That without modification of a Specific life-force there can be no specific variation.

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